Be supportive but not an enabler. Supportive as in helping them make a positive change in their lives, this could include making changes in the helper's life. Enabling is anything that makes it easier for the person to continue with their addiction, like loaning them money. Let them know about resources without trying to force the issue. Preaching, coercion, bribing, yelling are usually not effective ways to achieve a lasting change.
Clinical Hypnotherapist, Physical Therapist, Certified Zero Balancing practitioner